Map showing the sampling stations (•) where surface samples were collected during cruises aboard R/V <i>Cape Ferguson</i> over the period September 2011 to November 2013.

<p>Inshore monitoring stations, from north to south, are: Snapper Island, Fitzroy Island, High Island, Frankland Island, Dunk Island, Pelorus Island, Pandora Reef, Geoffrey Bay, Double Cone Island, Daydream Island, Pine Island, Humpy and Halfway Islands, Pelican Island, Barren Island, with separate colours representing separate regions as indicated in the legend. Yellow dots indicate mid- and outer-shelf reefs, from north to south: Mantis Reef, Wreck Bay, Fairway Channel, Shipping Channel, Tydeman Reef, Lizard Island, Arlington Reef, Twin Cays, Elusive Reef, Swains Reefs, Inner Swains.</p

Principal component analysis of carbonate chemistry data for four inshore regions of the Great Barrier Reef (GBR) over three different seasons.

<p>Data are contrasted to those from the mid- and outer-shelf reefs of the GBR. Inshore data were pooled over regions per sampling Visit.</p

Derived parameters at 14 inshore reefs during six research trips in four geographic regions along the length of the Great Barrier Reef.

<p>Ω_ar = Aragonite saturation state. The box denotes the inter-quartile range, whiskers denote 1.5× the inter-quartile range, the black line indicates the mean, and circles are outliers >1.5× the inter-quartile range.</p

Coral Reefs on the Edge? Carbon Chemistry on Inshore Reefs of the Great Barrier Reef

<div><p>While increasing atmospheric carbon dioxide (CO₂) concentration alters global water chemistry (Ocean Acidification; OA), the degree of changes vary on local and regional spatial scales. Inshore fringing coral reefs of the Great Barrier Reef (GBR) are subjected to a variety of local pressures, and some sites may already be marginal habitats for corals. The spatial and temporal variation in directly measured parameters: Total Alkalinity (TA) and dissolved inorganic carbon (DIC) concentration, and derived parameters: partial pressure of CO₂ (<i>p</i>CO₂); pH and aragonite saturation state (Ω_ar) were measured at 14 inshore reefs over a two year period in the GBR region. Total Alkalinity varied between 2069 and 2364 µmol kg⁻¹ and DIC concentrations ranged from 1846 to 2099 µmol kg⁻¹. This resulted in <i>p</i>CO₂ concentrations from 340 to 554 µatm, with higher values during the wet seasons and <i>p</i>CO₂ on inshore reefs distinctly above atmospheric values. However, due to temperature effects, Ω_ar was not further reduced in the wet season. Aragonite saturation on inshore reefs was consistently lower and <i>p</i>CO₂ higher than on GBR reefs further offshore. Thermodynamic effects contribute to this, and anthropogenic runoff may also contribute by altering productivity (P), respiration (R) and P/R ratios. Compared to surveys 18 and 30 years ago, <i>p</i>CO₂ on GBR mid- and outer-shelf reefs has risen at the same rate as atmospheric values (∼1.7 µatm yr⁻¹) over 30 years. By contrast, values on inshore reefs have increased at 2.5 to 3 times higher rates. Thus, <i>p</i>CO₂ levels on inshore reefs have disproportionately increased compared to atmospheric levels. Our study suggests that inshore GBR reefs are more vulnerable to OA and have less buffering capacity compared to offshore reefs. This may be caused by anthropogenically induced trophic changes in the water column and benthos of inshore reefs subjected to land runoff.</p></div

Biological, chemical and physical properties of water samples at the time of collection between 2011 and 2013.

<p>Average values for salinity (Sal.), temperature (Temp.), chlorophyll <i>a</i> (Chl <i>a</i>), ammonium (NH₄⁺), Nitrate/Nitrite (NO₃^–/NO₂^–) and phosphate (PO₄³⁻) and their amplitude (maximum minus minimum level) are shown. Standard deviations are shown for chlorophyll <i>a</i> and nutrient data; N: number of samples used to calculate the average.</p><p>Biological, chemical and physical properties of water samples at the time of collection between 2011 and 2013.</p

Relationships between salinity normalized dissolved inorganic carbon (DIC_S) and salinity normalized Total Alkalinity (TA_S) for the a) Wet-tropics, b) Burdekin, c) Whitsundays, d) Fitzroy and e) offshore shelf regions of the Great Barrier Reef.

<p>The regression lines and corresponding equations were obtained using model II linear regression. r²: coefficient of determination; p: significance level.</p

Measured Temperature, Salinity, Total Alkalinity (TA) and dissolved inorganic carbon (DIC) on 14 inshore reefs during six research trips in four geographical regions along the length of the Great Barrier Reef.

<p>The box denotes the inter-quartile range, whiskers denote 1.5× the inter-quartile range, the black line indicates the mean, and circles are outliers>1.5× the inter-quartile range.</p

Total Alkalinity (TA) and dissolved inorganic carbon (DIC) data for each island station, sorted from north to south, during each Visit and for each of the three Locations.

<p>Regions are colour coded as per <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0109092#pone-0109092-g001" target="_blank">Fig. 1</a>. Note that duplicates are plotted but in most cases cannot be distinguished because of the low between-duplicate variance.</p

Map of Australia, showing the two different regions in this study–the Great Barrier Reef on the North East coast, and the Kimberley region on the North West coast.

<p>Map of Australia, showing the two different regions in this study–the Great Barrier Reef on the North East coast, and the Kimberley region on the North West coast.</p

spAARS activity (nmol PPi hr^-1mg protein^-1) and spETS activity (μL O₂ hr^-1 mg protein^-1) in 3 size fractions (73–150 μm, >150 μm and >350 μm) of zooplankton samples collected from 5 cruises to the Kimberley coast, contrasting cruise differences.

<p>spAARS activity (nmol PPi hr^-1mg protein^-1) and spETS activity (μL O₂ hr^-1 mg protein^-1) in 3 size fractions (73–150 μm, >150 μm and >350 μm) of zooplankton samples collected from 5 cruises to the Kimberley coast, contrasting cruise differences.</p